Does not work :( Bewertet mit 2 von 5 Sternen

I am afraid that I regretfully have to amend my previous glowing review, because after a couple of reboots the extension no longer works. The "select next tab group" button does not activate when clicked, and the "Group your tabs" button is not populated unless you switch to each tab group in turn in the normal way.
It's such a shame - I thought this going to be an essential addon.
By the way, I am on Ubuntu 12.04, Firefox 18.0.2.